1. Field of the Invention
This invention relates to a digital weighing machine and more particularly a digital weighing machine utilizing change in capacitance.
2. Description of the Prior Art
There have been proposed weighing machines of new type capable of indicating weight in a digital manner which replaced the prior art according to which weight is visually indicated by means of a fixed scale plate in cooperation with a rotary pointer adapted to rotate in response to the weight or a rotary pointer adapted to rotate in response to the weight associated with a fixed pointer. In one type of such weighing machine, i.e., a digital weight control including a differential transformer and a strain gauge used as a sensor, displacement (voltage) representative of weight is converted to a digital amount through an A/D converter and a mechanism of the like for transmitting the weight to the sensor has to be adjusted for correction of linearity in order to maintain linearity of an output voltage of the sensor with respect to the weight. Thus the weighing machine becomes complicated and difficult to adjust. In addition, zero point has to be adjusted mechanically and manufacturing becomes complicated. There was also great restriction of reliability and price.
In another type of devices employing a photo-electric decoder or a mechanical system in which a pointer moving in response to the weight is caused to follow by means of an electric motor or a spring and amount of movement is converted in the form of pulses for counting, amount of change to a sensor actuated in response to the weight is converted through rack and pinion and there are many frictional portions in a transmitting mechanism. For this reason, such devices are disadvantageous in respect to accuracy and reliability and there has been no such devices as to demonstrate advantages of high reliability possessed by a digital electronic device.
It is an object of the present invention to preclude these drawbacks and to provide a digital weighing machine with high accuracy which is wear resistant and very easy to assemble and has less friction.
It is another object of the invention to provide a digital weighing machine without any A/D converter which counter is capable of correcting error in mechanism in respect to linearity of weight indication and has no necessity to adjust a zero point mechanically.